AB1489 VALIDATION OF QUANTITATIVE COMPUTER ANALYSIS OF ULTRASOUND IMAGES OF THE ACHILLES AND PATELLAR TENDONS IN HEALTHY SUBJECTS.
Authors: Á. Andreu-Suárez, C. Guillén-Astete, M. Tortosa-Cabañas
Journal: Annals of the Rheumatic Diseases (2022)

Background The ultrasound study of tendons is a component of the complementary evaluation of patients with different musculoskeletal pathologies, which include immune-mediated rheumatological diseases. Until now, the assessment of the ultrasound status of the tendons largely depends on the subjectivity of the explorer, following specific guidelines such as the fibers structure, their global echogenicity and their thickness. This evaluation is of great interest for the diagnose, however its role for the follow-up is not so clear as the subjective evaluation may not perceive subtle changes. Computerized image analysis has recently been introduced to complement the echographic evaluation. Two of the most useful parameters in this analysis are the mean and mode of gray intensities. Both allow a global evaluation of the echostructure of an organ based on the distribution of shades of gray and the highest concentration of a particular shade, without evaluating the organization pattern of the image obtained. Objectives To determine if computer analysis of static images is valid and suitable for its use in the study of tendons. Methods The ultrasound images of healthy volunteers were analyzed. The analysed tendons were: the body of the patellar tendon in transverse approach and the longitudinal section of the Achilles tendon, both of them from the dominant side. Image processing was performed using the ImageJ 1.53e program (Wayne Rasband &amp; contributors – NIH, USA). A gray spectrum analysis (0-255) was performed with the calculation of the mean, standard deviation (SD), range, median and mode. Two measurements of different cuts of the patellar tendon (at the point of emergence of the tibial plateau and 20 mm proximal to it) and three longitudinal cuts of 20 mm of the Achilles tendon (paramedial, central and paralateral) were used for the validation process of the analysis carried out by the software. Results Images from 44 healthy volunteers were analyzed: 20 men and 24 women. 44 Achilles tendon image trios and 44 patellar tendon image pairs were analyzed and their corresponding means and modes were compared as related variables. In the study of the Achilles tendon, according to the Shapiro-Wilk test, the distribution of the gray distribution means had a non-normal distribution while the modes had a normal distribution. The means ± standard deviation of gray intensity was: 80.15 ± 26.04, 80.05 ± 25.57 and 79.91 ± 25.83 for the medial, central and lateral slices, respectively (Friedman, P=.454; Bonferroni not applicable). The means of the modes of gray intensities for the same measures were 67.35 ± 31.60, 67.76 ± 32.18 and 68 ± 32.18, respectively (ANOVA paired data, P=.259; Bonferroni not applicable). In the patellar tendon study, all measurement distributions were non-normal. Mean gray intensity at the point of tendon emergence (P) was 81.35 ± 29.63 and at 20mm proximal to this point it was 80.97 ± 29.08 (Wilcoxon, P=.327). The means of the modes at the same locations were 82.71 ± 28.75 and at 20mm proximal to this point it was 64.44 ± 33.31 (Wilcoxon, P=.079). Figure 1. Image analysis of an Achilles tendon in the central longitudinal plane. Conclusion The quantitative analysis of static images of healthy tendons shows no differences between the same structures in longitudinal or transverse planes. Based on this validation test, the demonstration of sensitivity to change caused by any stimulus (sport, noxae or treatments) could allow its use as a complementary instrument for the assessment of tendinous structures over time. Disclosure of Interests África Andreu-Suárez: None declared, Carlos Guillén-Astete Speakers bureau: Novartis, Janssen, Abbvie, Grunenthal, UCB, Gebro, Paid instructor for: Roche, Novartis, Janssen, Esteve, Menarini, Consultant of: Janssen, Novartis, Roche, Grant/research support from: Pfizer, Grunenthal, Gebro, Novartis, Marina Tortosa-Cabañas: None declared